Page:First course in biology (IA firstcourseinbio00bailrich).pdf/164

 Examples are bean, morning-glory. The hop twines from the observer's right to his left, or with the sun.

—136. Set the pupil to watch the behavior of any plant that has tendrils at different stages of maturity. A vigorous cucumber plant is one of the best. Just beyond the point of a young straight tendril set a stake to compare the position of it. Note whether the tendril changes position from hour to hour or day to day. 137. Is the tip of the tendril perfectly straight? Why? Set a small stake at the end of a strong straight tendril, so the tendril will just reach it. Watch, and make drawing. 138. If a tendril does not find a support, what does it do? 139. To test the movement of a free tendril, draw an ink line lengthwise of it, and note whether the line remains always on the concave side or the convex side. 140. Name the tendril-bearing plants that you know. 141. Make similar observations and experiments on the tips of twining stems. 142. What twining plants do you know, and which way do they twine? 143. How does any plant that you know get up in the world? 144. Does the stem of a climbing plant contain more or less substance (weight) than an erect self-supporting stem of the same height? Explain.